Electron discharge device



Nov. 14, 1950 A. SOMMER 8 ELECTRON DISCHARGE DEVICE Filed Feb. 25, 1948IWT/MGNV- 0155/1 41 /nven7'Zr ALFRED SUMMER By OWMM Patented Nov. 14,1950 UNITED i PAT E N T F F l c E I Q I 2,529,888

-ELECH1-RON DISCHARGE DEVICE :Alfredfiommer, Iyer, England, assignor toElecktric &"'-Musical'-lndustries Limited, Hayes, MiddlesexfEnglanil-acompany of Great Britain ApplicationFebrua-ry 25, 1948, Serial No.10,941

-In .Greati-Britain June 29, 1946 Section -1,Piilili'c' Law 690, August8, 1946 *Patent' expires June 29, 1966 ioiclaim s. (01. 250165)eaftersreferredto asthe-l-riud described) havingian electrode"sensitised --so to be an: emitter: of photo-electrons or of secondarwelectrons (such electron'sbeing inthe-claims generically referred (to-asimpact electrons) -Suchsdevicesoomprise for example photoelectric-cellsand electron multipliers, and-television transmission'tubes em-..ploy-ing photo-sensitivev cathodes or photo-sensi- .;.tive.'rnosaic.screens.

. -.=In' one method ofmanufacturing suchsensitive electrodes after theenvelope of the device is -evacuated (and baked, -a-deposit rQf asuitable lmetal'such asa antimony ,is appliedcand subse ,quently asensitisingsubstance .such as caesium E -admitted to-rreact -with the,metal. TIt is .found that considerably lower sensitivitiesaare-.obtainedif an antimonydepositvisnexposed to,.air prior to asensitisation.compared withacases ,in t which v.no

exposureflis allowedtoqoccur. I

f 'Fnpwxamplq-wzhen the .cathode moi-la photoelectrioceH i'sfmadelbydepositing aH-layer of .anti'mony ,aiter the final evacuation ofthe enylope,..caesium.being. thereafter. admitted tore- "fact, with the-antimony,i, the sensitivity Lof ..the cathode, 'isL-usually between I50and 100 micro- ,amp'eres ,perglumen of incident ilight. When however,the. antimonydepos'it is exposedtoair .before the caesium.sensitisationaconsiderably lower .sensitiritiesare obtained, and maseries "of tests it "wasifoundithat after exposure of said deposit toair for a period of approximately'lb minutes before sensitisation, thefinalsensitivit'y was under-1120 'miicroamperes per lumen. It .isreasonable to assume that this. deleterious .effect .resultsfiromsuperficial oxidationof theanti- :mdfiy depositj ,mostsatisfactoryresults no baking; ofathe.v device eis efiected after the discharge ,inhydrogen.

.In .order that the invention maybe clearly understood and readilycarried into-effect, the

same will now be described with refere'nceato the accompanying drawing,wherein :Figureiil illustrates diagrammatically a fragment of anelectrode for a photo-electric cellzmanufactureid by a method accordingto oneexampleaof the present invention, and Figure '2 illustratesidia-.grammatically'onesta'ge of the method-according ,to said example.

In the illustrated example of the-invention applied to themanufacturerofravphotoeleotric. cell,

an antimony layer isudepositedon arsupport I 1 whichiissubsequentlywsealed intothe -envelope.:2

of the cell 'to form.agphotoeelectric:cathodegdur- .ing -which operationthe antimony-glayer :zisz-of course exposed to I air. The envelope'zcontaining the antimony-layer evacuated throughaahzreX- vhaust tube 3'andthereaiteybakedi in yacuumia't -a temperature of between 250C..-and--300' "C.

and, after cooling, hydro'genxis admitted-by the tuber3 into theenvelope of the cell 1 until ,a suitable pressure is? achieved,the'ypressurebeingtfor example of the'order of of.a'millimeter-oi iner-.cury. The antimony -layer is :ithen: connected :to the negativeterminaleof -.a--volt/age-'supply: 4' and en/suitable second-electrode5-Withinwthe envelope is connected rto-a :point-of-positive potential:to cause adischarge to occur in the-hydrogen; The

potential difference requiredxbetween said'elec- .trodes-wilrr-depend.uponra number of :factors,

.among .them. the pressurevin therenvelopeand -maybe for example 50.0-v0lts. u'Ihis; discharge 1 I Now it is often desirable in manufacturingsuch "device'stoexpose. the deposit to ,air .and .'.it ;is therefore theobject of thisinventionto=enable suchra depositto'be so exposed -without,.such .ex-

,posure seriously 1. affecting the ultimate ,photodeviceof-ithe-h-indedescribed wherein said sensitive electrode comprises a metal depositWhich has been exposed to air and wherein the deleterious effect of suchexposure which would otherwise result is reduced or substantiallyeliminated by subjecting said deposit to a discharge in -.;g I

hydrogen and then without further exposure to air saiddeposit issensitised in vacuo.

;,Preferably, said metalrcomprises antimony and the substance admittedtosensitise the :metal is maintained .for ashort time, for example one,minute or less, and-thethydrogenzis then remoyed from the envelope "byevacuation through the tube 3 andwhileimaintaining-the vacuum-sensiti--:sation is efiected by admitting caesium :to react -With .theeantimony,there a being-- no further baking before- ,said caesium sensitisation;vThe structureof the finalelectrode-isindicated in-Eigure 1 wherein-thereference numeral 6 indicates the rlayer of antimony :sensitised (withcaesium, gpro- -vided-- on the support I. Y Photo-electric cells,manufactured .by this methodwere found toh-avea sensitivityeof over 50microamperes per lumen-so that; harmful efiects of exposing the antimony,toair :had been substantially avoided.

elnta modification of the-m-ethod-tdescribeduin? stead of" applying apotential. difference vbetween the .cathode and acsecondelectrodeinorder to pause the discharge in hydrogen ,to' o ccur; the :dischargeiscausedto occur byplacing the-device lire-ahighfrequencyoscillatoryfieldegenerated: by

comprises caesium, and in order to obtain the =means of a suitable highfrequency oscillator.

The invention has been described as applied to the manufacture ofphoto-electric cells but it will be understood that it can also beapplied to the manufacture of electron multipliers, having electrodessensitised so as to be secondary electron emitters, and to themanufacture of television transmission tubes having photo-cathodes orphoto-sensitive mosaic screens.

What I claim is:

1. A method of producing an electron discharge device having anelectrode sensitised to be an emitter of impact electrons, including thesteps of depositing metal under conditions involving exposure to air,subjecting the metal deposit to an electric discharge in hydrogen,whereby eifects of exposure to air are reduced, and sensitisin saiddeposit in vacuo before exposure to air.

2. A method of producing an electron discharge device comprising anevacuated envelope containing an electrode sensitised to be an emitterof impact electrons, including the steps of depositing metal on asupport under conditions involving exposure to air, placing said supportin an envelope, evacuating said envelope, admitting hydrogen to saidenvelope, establishing an electric discharge in said hydrogen to exposesaid metal deposit to the discharge, evacuating the hydrogen from saidenvelope, and sensitising said metal deposit in vacuo before exposure toair.

3. A method of producing an electron discharge device having anelectrode sensitised to be an emitter of impact electrons, including thesteps of depositing antimony under conditions involving exposure to air,subjecting the antimony deposit to an electric discharge in hydrogen toeliminate substantially deleterious eifects of exposure to air, andexposing said deposit to -'caesium vapor in vacuo before exposure to airto sensitise' the deposit.

4. A method of producing an electron discharge device comprising anevacuated envelope containing an electrode sensitised to be an emitterof impact'electronsincluding the steps of decontaining an electrodesensitised to be an emitter of impact electrons, including the steps ofdepositing antimony on a support outside an en- 'velope, -placing saidsupport in the envelope,

evacuating said envelope, admitting hydrogen to the envelope,establishing an electric discharge in the hydrogen to expose saidantimony deposit to the discharge, evacuating hydrogen from saidenvelope, and admitting caesium vapour to said envelope to sensitisesaid antimony deposit before exposure to air.

6. A method of producing an electron discharge device comprising anenvelope containing an electrode sensitised to be an emitter ofelectrons, including the steps of depositing metal on a support underconditions involving exposure to air,

placing said support in an envelope, locating an electrode in saidenvelope and spaced from said support, evacuating said envelope,admitting hydrogen to said envelope, applying relatively high and lowpotentials to said electrode and said deposit respectively to establishan electric discharge in said hydrogen, evacuating the hydrogen fromsaid envelope, and sensitising said metal deposit in said envelope invacuo before exposure to air.

7. A method of producing an electron discharge device comprising anevacuated envelope containing an electrode sensitised to be an emitterof impact electrons, including the steps of depositing antimony on asupport under conditions involving exposure to air, placing said supportin an envelope spaced from an electrode therein, evacuating saidenvelope, admitting hydrogen to said envelope, applying relatively highand low potentials to said electrode and said deposit respectively toestablish an electric discharge in said hydrogen, evacuating thehydrogen from said envelope, and admitting caesium vapor to saidenvelope to sensitisesaid antimony deposit before exposure to air.

8. A method of producing an electron discharge device comprising anenvelope containing an electrode sensitised to be an emitter of impactelectrons, including the steps of depositing metal on a support underconditions involving exposure to air, placing said support in anenvelope, evacuating said envelope, admitting hydrogen to said envelope,producing a high fre-- quency oscillatory field in the region of saidenvelope to cause an electric discharge in the envelope in the presenceof the hydrogen, evacuating the hydrogen from the envelope, andsensitising the metal deposit in said envelope in vacuo before exposureto air.

9. A method of producing an electron discharge device comprising anevacuated envelope containing an electrode sensitised to be an emitterof impact electrons, including the steps of depositing antimony on asupport under conditions involving exposure to air, locating saidsupport in an envelope, evacuating said envelope, admitting hydrogen tosaid envelope, producing a high frequency oscillatory field in theregion of said envelope to cause an electric discharge in the envelopein the presence of the hydrogen, evacuating the hydrogen from theenvelope, and admitting caesium vapour to said envelope to sensitisesaid antimony deposit before exposure 'to air.

10. A method of producing an electron discharge device comprising anevacuated envelope containing an electrode sensitised to be an emitterof impact electrons, including the steps of depositing antimony on asupport under conditions involving exposure to air, locating saidsupport in an envelope, evacuating said envelope, admitting hydrogen tosaid envelope, establishing an electric discharge in the hydrogen toexpose said antimony deposit to the discharge, evacuating hydrogen fromthe unbaked envelope, and admitting alkali metal vapour to. saidenvelope to sensitise said antimony deposit before exposure to air. V

ALFRED SOMMER..

I REFERENCES CITED' The following references are" of record in the fileof this patent:

UNITED STATES PATENTS

